More ba­bies born via ce­sare­an sec­tion grow up to be heavy chil­dren and teens than those de­liv­ered vagi­nal­ly, ac­cord­ing to a new study of more than 10,000 UK in­fants.

Eleven-year-olds de­liv­ered by C-sec­tion, for ex­am­ple, were 83 per cent more like­ly to be over­weight or obese than their vagi­nal­ly-born peers once oth­er re­lat­ed fac­tors–such as their moth­er's weight and how long they were breast­fed–were tak­en in­to ac­count.

The find­ings are in line with a re­cent re­view of nine ear­li­er stud­ies that al­so found a link be­tween C-sec­tions and child­hood obe­si­ty.

With C-sec­tions, "there may be long-term con­se­quences to chil­dren that we don't know about," said Dr Jan Blus­tein, who led the new study at the New York Uni­ver­si­ty School of Med­i­cine.

The rate of C-sec­tions in the US has been ris­ing, lead­ing to con­cerns about pos­si­ble com­pli­ca­tions for moth­ers and ba­bies. Ac­cord­ing to the Cen­ters for Dis­ease Con­trol and Pre­ven­tion, C-sec­tions ac­count­ed for al­most one in three births in 2010–up from one in five in 1996.

For women, the pro­ce­dure in­creas­es the chance of bow­el or blad­der in­juries as well as fu­ture preg­nan­cy com­pli­ca­tions.

Blus­tein said the size of the obe­si­ty risk for kids is "not great," and shouldn't come in­to play for women who need a C-sec­tion for med­ical rea­sons.

But, "a woman who's con­sid­er­ing C-sec­tion elec­tive­ly should prob­a­bly know about those risks," she told Reuters Health.

The re­searchers analysed da­ta from ba­bies born in Avon, UK in 1991 and 1992 who were fol­lowed through age 15. Just over nine per cent of the in­fants were de­liv­ered via C-sec­tion.

On av­er­age, kids de­liv­ered by C-sec­tion were born slight­ly small­er–by less than two ounces–than those who went through vagi­nal birth.

Start­ing at six weeks of age, how­ev­er, C-sec­tion ba­bies were con­sis­tent­ly heav­ier than vagi­nal­ly-born in­fants at al­most all check-ins. That link was es­pe­cial­ly strong among chil­dren born to over­weight moth­ers, Blus­tein and her col­leagues re­port in the In­ter­na­tion­al Jour­nal of Obe­si­ty.

Across the whole study group of chil­dren, rates of over­weight and obe­si­ty ranged from 31 per cent at age three to 17 per cent at ages sev­en and 15.

Blus­tein said stud­ies haven't been able to prove whether C-sec­tion, it­self, is a rea­son some ba­bies tend to gain more weight.

If it is, she spec­u­lates, it might have some­thing to do with C-sec­tion ba­bies miss­ing out on im­por­tant ex­po­sures to friend­ly bac­te­ria dur­ing the trip through the birth canal.

"Gen­er­al­ly, the ear­ly coloni­sa­tion and es­tab­lish­ment of the in­tes­tine with bac­te­ria seems very im­por­tant. Yet, much more work is need­ed be­fore we can ex­plain the mech­a­nisms of the ear­ly bac­te­r­i­al coloni­sa­tion," Tere­sa Ajslev, from the In­sti­tute of Pre­ven­tive Med­i­cine in Fred­eriks­berg, Den­mark, told Reuters Health in an e-mail.

For ex­am­ple, there may be a spe­cif­ic type of bac­te­ria that's pro­tec­tive, said Ajslev, a re­searcher and PhD stu­dent who has stud­ied preg­nan­cy-re­lat­ed im­pacts on child­hood weight but wasn't in­volved in the new re­port.

Or bac­te­ria im­bal­ances could more gen­er­al­ly dis­rupt in­testi­nal func­tion in a way that pro­motes obe­si­ty.

Ei­ther way, if the ex­act cause could be iden­ti­fied, it might be pos­si­ble to give C-sec­tion ba­bies dos­es of the miss­ing gut bugs to re­store bal­ance.

But it's al­so pos­si­ble bac­te­ria have noth­ing to do with the obe­si­ty link to C-sec­tion births.

"The oth­er pos­si­bil­i­ties are (that) these are chil­dren that would have been heav­ier any­way," Blus­tein said.

"Be­ing heavy as a woman is a risk fac­tor for C-sec­tion, so that's the prob­lem with try­ing to fig­ure out whether this is re­al or if it's sim­ply a mat­ter of se­lec­tion," since over­weight par­ents are more like­ly to have over­weight chil­dren.

Her study was able to take a moth­er's weight in­to ac­count, and did find the link be­tween C-sec­tion births and child obe­si­ty was "weak" among chil­dren born to nor­mal-weight moth­ers.

But there could be oth­er un­mea­sured fac­tors that help ex­plain the over­all link be­tween de­liv­ery method and a child's weight.

"This cer­tain­ly is not the last word," Blus­tein said. (Reuters)

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